1. Field of the Technology
The present technology relates to reduction in cost of a compound semiconductor device epitaxial growth substrate which is manufactured through epitaxial growth, and in particular, to reduction in cost of a semiconductor device such as a high efficiency multijunction-type compound solar cell. In addition, the present disclosure relates to reduction in cost of a semiconductor substrate that is used for epitaxial growth by reusing the substrate.
2. Description of the Background Art
For a semiconductor device with a large amount of epitaxial films having a large area, such as a solar cell, it is required that the material cost be as low as possible. The material cost of the substrate is large. Therefore, ideas for reducing the material cost by techniques such as reusing the substrate after peeling the substrate from the element have been put forth for a long time.
A conventional method of substrate reuse is known in which pores are formed in, for example, the surface of a substrate. Subsequently, an element layer is epitaxially grown, and a great number of voids which exist in the portion where the pores have been formed (middle layer) are cut through so as to mechanically separate the substrate from the element layer. According to this method, however, the pores remain on the surface of the substrate, and therefore, flattening or cleaning (e.g., through surface processing) becomes necessary.
In another conventional substrate removal method an atom displaced layer is formed in a portion that is extremely shallow from the surface of the substrate, by means of ion implantation. Subsequently, an element layer is epitaxially grown and the atom displaced layer (middle layer) is cut through so as to mechanically separate the substrate from the element layer, and thereby, the substrate is reused. According to this method, however, the surface of the substrate is damaged, and therefore, flattening or cleaning through surface processing becomes necessary
Yet another conventional method of substrate removal involves epitaxially growing an element layer after a middle layer (that can be selectively etched) has been formed on the surface of the substrate. The middle layer is etched and removed, and thereby, the substrate and the element layer are separated from each other through chemical treatment. According to this method, however, a layer that has deteriorated due to a chemical change remains on the surface of the substrate, and therefore, flattening or cleaning through surface processing, again, becomes necessary.
As described above, the conventional technology for reusing a substrate has a problem in that the surface of the substrate becomes coarse or polluted after the separation, and requires processing for flattening or cleaning, such as polishing on the surface of the substrate, lapping or the like. Therefore, the cost increases, due to surface processing. In addition, a problem arisesin that the number of times that use is possible is reduced due to reduction in the thickness of the substrate, and thus the yield is reduced due to cracking of the substrate.
Example documents that disclose conventional technologies concerning the present technology include the following: Electron Lett. 35, p. 1024, by B. Asper et al. (1999), Appl. Phys. Lett. 76, p. 2131, by J Schermer et al. (2000) and 19th European Photovoltanic Solar Energy Conference, 7-11, June 2004, Paris, France, p. 169-172 by M. M. A. J. Voncken et al. (2004).
The present technology is provided in order to solve the aforementioned problems. An object of the technology is to provide a compound semiconductor device epitaxial semiconductor growth substrate where an element layer can be formed through epitaxial growth again after the substrate and the element layer that has been epitaxially grown have been separated from each other without causing (1) an increase in the cost due to surface processing of the substrate, such as polishing or lapping, (2) a reduction in the number of times that use is possible due to reduction in the thickness of the substrate, or (3) reduction in the yield due to cracking of the substrate, as well as a semiconductor device that uses such a substrate, and a manufacturing method of the same.